Commentary: Proposed bonfire ban is not based in sound science

April 08, 2013|By Thomas Eastmond

As the Great Bonfire War of 2013 continues, we can agree to one thing: If beach fire rings really do generate demonstrably dangerous levels of particulate matter (PM2.5) emissions, they probably need to go or be reduced ("Fire ring hearing may be delayed," April 7).

How much PM2.5 do the fire rings actually generate?

Curiously, that's the one question the South Coast Air Quality Management District (AQMD) seems determined not to answer.

The AQMD's standards provide that an emissions source is significant if it raises particulate concentrations at nearby "sensitive receptors" — residences and similar sites — by at least 2.5 micrograms per square meter (ug/m3). This can easily be measured near the fire rings.

Yet AQMD hasn't done so.

Why? In litigation, there's a rule that when a person has the power to introduce a type of evidence that could be conclusive — but doesn't — it's a reasonable conclusion that the evidence doesn't say what he wants it to say.

A regulatory agency's task is to identify truly significant risks, weigh the costs and benefits and adopt an appropriate response. Agencies generally consider an activity's risk significant if it increases the lifetime risk of harm by one chance in a thousand. Regulations based on speculative or remote harms beyond this threshold may be overturned as arbitrary.

So how do the fire rings affect regional air quality? Their effect is negligible — a rounding error.

Using emissions factors for firewood (that is, the mass of emissions per mass of fuel) taken from peer-reviewed studies, and using reasonable estimates of wood consumption and fire-ring use rates, yields a total figure of about 30 pounds annualized daily average of PM2.5 for all the fire rings in the South Coast basin — about .001% of the 143 tons emitted daily (directly and indirectly) from all sources. By comparison, restaurants charbroiling hamburgers generate several tons of PM2.5 per day.